Near field communication (NFC) devices are being integrated into communication devices, such as mobile devices to provide an example, to facilitate the use of these communication devices in conducting daily transactions. For example, instead of carrying numerous credit cards, the credit information provided by these credit cards could be stored onto an NFC device. The NFC device is simply tapped to a credit card terminal to relay the credit information to the terminal to complete a transaction. As another example, a ticket writing system, such as those used in a bus or train terminal, may simply write ticket fare information onto the NFC device instead of providing a ticket to a passenger. The passenger simply taps the NFC device to a reader to ride the bus or the train without the use of a paper ticket.
Generally, NFC requires that NFC devices be present within a relatively small distance from one another so that their corresponding magnetic fields can exchange information. Typically, a first NFC device transmits or generates a magnetic field modulated with the information, such as the credit information or the ticket fare information. This magnetic field inductively couples the information onto a second NFC device that is proximate to the first NFC device, which is received by an antenna of the second NFC device. The second NFC device may respond to the first NFC device by inductively coupling its corresponding information onto an antenna of the first NFC device.
However, in the field of NFC there is an increasing diversity of products, specifically in terms of the effective area of antennas. In particular, there is strong demand for solutions using ever smaller antennas. Therefore, NFC devices are being implemented having increasingly small antennas, despite a common desire to interoperate with legacy devices, which generally have larger antennas, and to pass test specifications defined with these larger antennas.
The disparity in antenna size generally results in poor magnetic coupling between the small and large antennas, which inhibits the ability to pass energy from one antenna to the other. This problem of energy transfer is compounded at low magnetic fields when the device with the small antenna is attempting to transmit using load modulation.
Additionally, a voltage associated with a response signal may vary depending on the distance between the first and second NFC devices, which in turns varies the magnetic coupling between these NFC devices. A large distance between the devices generally causes the received response signal to have a small voltage, and thus a poor magnetic coupling may result between the devices.
Several problems generally arise when NFC devices experience poor magnetic coupling. For example, when only a small portion of energy transmitted from the first NFC device is actually received by the second NFC device, it becomes difficult for the second NFC device to be able to power itself from the magnetic field. Further, poor magnetic coupling may inhibit the NFC devices' ability to perform load modulation because the second NFC device may only be able to effect a small portion of the total energy that was actually transmitted by the first NFC device. Thus, the net effective energy recognized back the first NFC device may be relatively small.
Thus, a need exists for NFC devices that are capable of communicating with one another even in the presence of poor magnetic coupling.
Embodiments of the disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number